Burners for high-temperature industrial applications

Hlavnou náplňou danej práce je priblíženie rôznych typov horákov a ich súčastí. Dôraz sa kladie najmä na spaľovací proces s obsahom kyslíku viac ako 21 %, v spaľovacom vzduchu. V anglickej terminológii je tento proces označovaný ako „oxygen-enhanced combustion“ (OEC). Práca sa zameriava na jeho charakteristiku, možnosti a vhodnosť jeho použitia. Keďže pri manipulácii s kyslíkom hrozí určité nebezpečenstvo zranenia, práca sa zameriava aj na posúdenie bezpečnosti a rizík s tým spojenými. Vzhľadom na to, že proces spaľovania za podmienok OEC sa výrazne odlišuje od podmienok spaľovania s atmosférickým vzduchom, v práci je vypracovaná aj analýza vplyvu obsahu kyslíka v atmosférickom vzduchu na adiabatickú teplotu plameňa a spotrebu paliva.The main purpose of the bachelor thesis is the discussion of different types of burners and their components. Emphasis is placed mainly on the combustion process with oxygen content more than 21 % in the combustion air, the so called oxygen-enhanced combustion (OEC). The thesis describes characteristic features, possibilities and appropriateness of its use. Since in handling of oxygen there is a level of risk of injury, the thesis also assesses the safety and risks associated therewith. As the combustion process in terms of OEC is significantly different from the conditions of combustion with the atmospheric air, the thesis analyses the impact of the content of oxygen in atmospheric air on flue gas temperature and fuel consumption.

Modelling of oxygen-enhanced combustion process

Hlavnou náplňou danej práce je matematické modelovanie procesu spaľovania, pri ktorom má spaľovací vzduch obsah kyslíka viac ako 21%, v anglickej terminológii označovaného ako „oxygen-enhanced combustion“(OEC) a jeho porovnanie s experimentálnymi meraniami. Práca sa venuje popisu procesu spaľovania ako aj charakterizácii OEC. Vzhľadom na to, že pri OEC sa pracuje s čistým kyslíkom, je časť práce venovaná aj nebezpečenstvám a nutnej bezpečnosti pri práci s ním. Práca obsahuje detailný popis spaľovacej komory, ako aj súčastí potrebných na prevádzku OEC. V práci sú dve sťažené časti, a to experiment a simulácia. Významnou časťou práce je teda počítačový model danej spaľovacej komory, ako aj simulácia procesu spaľovania s prídavným kyslíkom pomocou využitia CFD metód. Numerické výsledky boli porovnané s experimentálnymi dátami - konkrétne rozloženie tepelných tokov do stien spaľovacej komory a rozloženia teplôt v plameni v horizontálnej rovine symetrie spaľovacej komory.The main purpose of the master´s thesis is the experimental study and the mathematical modelling of the combustion process in which the combustion air is enriched with the high-purity oxygen, i.e. the oxygen content is more than 21 %. This combustion technology is called as the oxygen-enhanced combustion (OEC). Since the experimental work required the manipulation with the pure oxygen, a part of the thesis is focused on risks and necessary safety associated therewith. The detailed description of the combustion chamber as well as of the components necessary for the operation of OEC is included. The main part of the thesis is the computational model of the combustion chamber and the simulation of OEC using CFD methods. The numerical results were then compared with the experimental data acquired during the combustion tests, namely the heat flux distribution along the combustion chamber and the distribution of in-flame temperatures in the horizontal symmetry plane of the chamber.

Evaluation of the technical condition of medium-sized boilers

The recent trend in the steam and electricity production has been both to increase the efficiency of the facility and to keep tightening legislation concerning emission limits. The lifetime of energy equipment is greatly influenced by the operating temperature, pressure and operating characteristics. The new conditions lead the operator to more often changes of these parameters, which has negative influence to the facility in terms of service life. Precise knowledge of the facility being operated and the ability to predict the residual life of its key parts in time is therefore necessary. A new methodology for determining the residual life and evaluating problematic situations of medium size boilers was developed at Brno University of Technology. Its approaches and advantages will be presented in this paper. The methodology provides the user with approaches for the lifetime evaluation of an equipment as a whole, based on detailed knowledge of the equipment being investigated and the ongoing damage. Additionally, if the equipment is continuously evaluated, it is possible to extend the inspection interval or to achieve a significantly higher lifetime of the entire equipment, thereby reducing the economic cost. If defined criteria are met, the methodology also allows inclusion of FEM and CFD simulations for achieving higher relevance of the results

Thermal load non-uniformity estimation for superheater tube bundle damage evaluation

Industrial boiler damage is a common phenomenon encountered in boiler operation normally which usually lasts several decades. Since boiler shutdown may be required because of localized failures, it is crucial to predict the most vulnerable parts. If damage occurs, it is necessary to perform root cause analysis and devise corrective measures (repairs, design modification, etc.). Boiler tube bundles, such as those in superheaters, preheaters and reheaters, are the most exposed and often the most damaged boiler parts. Both short-term and long-term overheating are common causes of tube failures. In these cases, the design temperatures are exceeded, which often results in decrease in remaining creep life. Advanced models for damage evaluation require temperature history, which is available only in rare cases when it has been measured for the whole service life. However, in most cases it is necessary to estimate the temperature history from available operation history data (inlet and outlet pressures and temperatures etc.). The task may be very challenging because of the combination of complex flow behavior in the flue gas domain and heat transfer phenomena. This paper focuses on estimating thermal load on superheater tubes via Computational Fluid Dynamics (CFD) simulation of flue gas flow including heat transfer within the domain consisting of a furnace and a part of the first stage of the boiler

Transient Thermal Stress Calculation of a Shell and Tube Condenser with Fixed Tubesheet

The present article deals with transient thermal stress calculation on a safety horizontal shell and tube condenser. This condenser is used in a power plant for cooling of hot steam diverted from the turbine in the case of its emergency shutdown. The standard stress calculation was provided according to the EN 13445 standard in steady regime. As consistent with this calculation, an expansion joint must be used on the shell. The main aim of this article is to describe a detailed calculation of the transient temperature field on the shell and tubes, using finite element method analysis, and longitudinal thermal stresses on the shell and tubes during the start-up process. Transient analyses are useable for more accurate EN 13445 calculation and, furthermore, for fatigue calculation

Modelling of oxygen-enhanced combustion process

The main purpose of the master´s thesis is the experimental study and the mathematical modelling of the combustion process in which the combustion air is enriched with the high-purity oxygen, i.e. the oxygen content is more than 21 %. This combustion technology is called as the oxygen-enhanced combustion (OEC). Since the experimental work required the manipulation with the pure oxygen, a part of the thesis is focused on risks and necessary safety associated therewith. The detailed description of the combustion chamber as well as of the components necessary for the operation of OEC is included. The main part of the thesis is the computational model of the combustion chamber and the simulation of OEC using CFD methods. The numerical results were then compared with the experimental data acquired during the combustion tests, namely the heat flux distribution along the combustion chamber and the distribution of in-flame temperatures in the horizontal symmetry plane of the chamber

Advanced Methods for Damage Evaluation of Boiler Tube Bundles

Dizertačná práca sa zaoberá aplikáciou pokročilých metód hodnotenia poškodenia trubkových zväzkov v kotloch so zameraním na poškodenie vplyvom teploty. Cieľom je navrhnúť postup riešenia problematiky a ukázať možnosti moderných prístupov. Práca popisuje rôzne typy poškodenia, ktoré sa môžu objaviť v priemyselných kotloch. Hlavný dôraz je kladený na najexponovanejšie a často aj najviac poškodzované časti, ktorými sú trubkové zväzky, napríklad prehrievače pary. Keďže poškodenie zariadenia je nežiaduce a často vedie k úniku média, poprípade až k odstávke, je nutné rýchlo reagovať a čo najskôr odhaliť príčinu a zabezpečiť nápravu. Jednotlivé typy poškodenia sú rozdelené do piatich základných skupín podľa mechanizmu poškodzovania. Jedným z najvýznamnejších vplyvov na životnosť má teplota zapríčiňujúca krátkodobé alebo dlhodobé prehriatie trubkových zväzkov. Tento typ poškodenia, znižujúci creepovú životnosť, nastane pri prekročení návrhovej teploty. Pre určenie poškodenia vplyvom teploty je však potrebná história reálnej povrchovej teploty zväzku trubiek, ktorá však pri zariadeniach často chýba. Pri hodnotení poškodenia je preto nutné potrebné teploty dopočítať na základe dostupných informácií (vstupné a výstupné teploty a tlaky atď.). To však môže byť zložité z dôvodu kombinácie komplexného prúdenia pracovných látok (najmä spalín) a prenosu tepla. V práci sú s ohľadom na dostupné dáta navrhnuté postupy a metódy prístupu pre získanie požadovaných informácií pre vyhodnotenie creepovej životnosti kotla. V prvom kroku navrhovaného postupu je vykonaný tepelne-hydraulický výpočet a následne určené teplotné zaťaženia trubiek prehrievača kotla pri spaľovaní zemného plynu s využitím CFD simulácie. V ďalšom kroku je určená povrchová teplota trubiek využitá pre výpočet poškodenia vplyvom teploty so zameraním na odhad creepovej životnosti. Nakoľko životnosť je v značnej miere ovplyvňovaná nedokonalosťami, v závere práce je zhodnotený vplyv oxidovej vrstvy na vnútornej strane trubky, ako aj vrstvy nánosov na strane vonkajšej.This thesis is focused on the application of advanced methods for evaluating damage to boiler tubes, specifically temperature related damage. The aim of this work is to develop an improved damage evaluation procedure utilizing capabilities of modern approaches. This work describes various types of industrial boiler damage. The main focus is on the most exposed and often the most damaged parts of boilers, which are tube bundles (for example, superheaters). Equipment damage is undesirable and often leads to leakages or even to the boiler shutting down. Therefore, it is necessary to find the problem as soon as possible and make the required changes to prevent further damage. The damage types are divided into five categories based on the damage mechanism. Temperature has one of the biggest influences on damage and it may cause short-term or long-term overheating in the tube bundles. This type of damage occurs when the designated temperature is exceeded and results in reduced creep life. It is necessary to know the real surface temperature history of the tube bundle to estimate temperature related damage, however this is often not available. Therefore, it is necessary to calculate those temperatures based on the available data (i.e. inlet and outlet temperatures and pressures). This is real challenge due to the combination of complex flows of the working substances (mainly flue gasses) and heat transfer. Considering available data, new approach is proposed in order to obtain information required for residual creep life estimation. In the first step, thermal – hydraulic calculation is performed followed by a thermal load estimation of a superheater tube bundle in a natural gas fired boiler, using CFD simulations. In the next step, the surface temperature is evaluated and used to determine the temperature related damage, specifically the creep life estimation. The life expectancy is in some ways influenced by imperfections, and therefore at the end of this thesis the influence of the oxide layer on the inner side of tube and fouling on outer side of tube is described.

Evaluation of the technical condition of medium-sized boilers

The recent trend in the steam and electricity production has been both to increase the efficiency of the facility and to keep tightening legislation concerning emission limits. The lifetime of energy equipment is greatly influenced by the operating temperature, pressure and operating characteristics. The new conditions lead the operator to more often changes of these parameters, which has negative influence to the facility in terms of service life. Precise knowledge of the facility being operated and the ability to predict the residual life of its key parts in time is therefore necessary. A new methodology for determining the residual life and evaluating problematic situations of medium size boilers was developed at Brno University of Technology. Its approaches and advantages will be presented in this paper. The methodology provides the user with approaches for the lifetime evaluation of an equipment as a whole, based on detailed knowledge of the equipment being investigated and the ongoing damage. Additionally, if the equipment is continuously evaluated, it is possible to extend the inspection interval or to achieve a significantly higher lifetime of the entire equipment, thereby reducing the economic cost. If defined criteria are met, the methodology also allows inclusion of FEM and CFD simulations for achieving higher relevance of the results

Computation of temperature field by cell method and comparing with commercial software

This paper deals with the temperature field of the shell and tube heat exchanger with segmental baffles. Two different types of shell and tube heat exchangers were analysed by a numerical model for thermal-hydraulic rating called the cell method. The cell method is a numerical computational model for calculating of temperature field of a shell and tube heat exchanger with segmental baffles. A huge benefit of the cell method is especially its simplicity. The computation of temperature field by the cell method is very fast and without the necessity of powerful hardware accessories. For analyses, two different types of shell and tube heat exchangers with segmental baffles were used. First, a co-current flow heat exchanger with a floating head and second a counter-current flow heat exchanger with a fixed tubesheet. Both analysed heat exchangers are horizontal, have one tube and one shell pass and segmental baffles. The results from cell method were compared with results from the HTRI, which is one of the most widely used commercial software for solving thermal-hydraulic rating of heat exchangers. The scope of this paper is to assess how exact the cell method is and if its results are useful for a mechanical design of shell and tube heat exchanger with segmental baffles